The MH lamp is a type of high intensity discharge (HID) lamp in which most of the light is produced by radiation of metal halide and mercury vapors in the arc tube. In 1961, Gilbert Reiling patented the first metal halide (MH) lamp but discharge lighting can trace its roots all the way to the 1800's when Sir Humphrey Davy demonstrated a discharge lamp. This first metal halide lamp demonstrated an increase of lamp efficacy and color properties over Mercury Vapor, which made it more suitable for commercial, street and industrial lighting. These lamps are available in clear and phosphor-coated lamps. The MH is currently the predominate light source for high bay lighting applications and typically has efficacy of 70-90 lm/W.
The ubiquitous use of high bay metal halide lights is common because they are relative efficient light sources and there is currently no viable alternative to reproduce similar light levels from a compact source of tens of thousands of lumens. The widespread use happens despite the fact that this type of light source can consume a great deal of energy. MB and other HID lamps are highly compact sources of light that require special power supplies or ballasts to provide a regulated supply of electricity for starting and maintaining a constant current during bulb operation. Since the metal halide bulbs invention in the 1960's additional improvements of the metal halide lighting have centered on the ballast technology. This has lead up to the most current ballast improvements of digital ballasts introduced only at end of the last century. Even with the recent ballast technology advances that have shown pulse start and digital ballast to be more efficient than magnetic ballasts, adoption is slow since digital ballasts cost 6× more than magnetic ballasts. Overall there is no indication that the MH bulb technology will see significant advances in efficacy in the coming years. Also the HID/MH lamps and their arc tubes operate at extremely high temperatures and can shatter if adequate precautions are not taken. This is compounded by the fact that MH bulbs can act as radiant heaters heating the surrounding air. and this heat must be extracted by HVAC exasperating rising energy costs.
It is believed that one day solid state lighting (SSL) will be capable of competing with HID and MH lighting. As of today SSL alternatives suffered from low LED efficacy and thermal management issues. Recently alternative lamp sources have begun to make in-roads in the market for high bay lighting. The Linear Florescent Lamps (LFL) in the form of super T8 and T5 bulbs have been introduced for gaining energy savings. This alternative product selection comes with issues such as reduced lumen output at room temperatures above 68° F. and typically 6× the maintenance cost of a metal halide fixture. It is anticipated that the fluorescent technologies are an intermediate step to the eventual adoption of SSL. Alternatives to the MH are High Pressure Sodium (HPS) and Low Pressure Sodium (LPS) but these lamp sources have begun to be phased out due to limited lifetime, poor CRI and expensive bulb replacement. Also MH bulbs typically burn out every 10-12K hours driving US building owners to replace millions of metal halide bulbs annually.
The area of high bay lighting to date has seen little penetration by LED Luminaries that are direct fixture replacements of metal halide fixtures. The current products offered are large heavy light sources that are typically more then 10-100× more expensive than the existing metal halide fixture. One issue with LED high bay fixture replacement has to date been how to recreate light patterns and levels of existing MH fixtures. Due to thermal design the LED luminaries typically have large square flat light sources consisting of many LEDs. This complicates optical design and how to most effectively design LED luminaries that can recreate comparable color temperature, light distribution and light intensity so that preexisting building electrical grids can be preserved. Also since the light output per LED is limited by thermal design the number of LEDs to produce greater than ten thousand lumens makes the luminaire 10× more expensive than typical MH fixtures.
In this patent a new type of light source termed an Integrated LED Fixture (ILF) is disclosed that can act as a direct metal halide bulb replacement. A ILF design that can replace the MH bulb instead of the entire fixture is ideal for many reasons including but not limited to reduced cost, and ease of instillation. The current prior art leaves makes it difficult to achieve the goal of creating a MH bulb replacement. First compact LED arrays with high luminous flux capable of extreme brightness are not commercially available. This extreme brightness can be defined as a small emission area such as one square inch that is capable of greater than 10,000 lm. This type of LED modules that produce tens of thousands of lumens could be widely applicable to streetlighting, highbay lighting, or even automotive lighting. The extreme brightness LED light modules are limited in commercial viability due to lack of thermal management systems that can keep the LED dies below a maximum junction temperature. The current invention solves these issue and makes the retrofit example viable.
In industrial and commercial space when MH bulb replacements occur the electrical grid and the necessary floor lighting pattern pre-exists and is expensive to alter. Consequently, in order to provide a retrofit compatible integrated LED lamp the light source must produce the same lumen output and similar illumination pattern on the floor. If the LED light source can be made into a dense array then simple glass or acrylic secondary optics can be used to shape the light to match previous metal halide light distribution. With an extreme brightness array a modular system can be arrived at where a single LED source can provide many different beam diameters and shapes.
The most typical high bay light based on metal halide bulb technology can produce 15,000-20,000 mean lumens for the right illumination level at a work surface 3-30 foot candle depending on mounting height. Thus for a LED light source with a efficacy of 80-100 lm/W a typical thermal heat flux could range from 150-250 W. This thermal energy comes in the form of phonons moving through a semiconductor lattice and must be handle through conduction from the back of the LED package. This electrical energy is typically only half the energy utilized by a metal halide bulb of equivalent lumen count but within the metal halide bulb the waste heat energy (˜90% of the energy) is released by electromagnetic radiation. Further complications exist in the fact that fans are not permitted in high bay lighting applications due to reliability and noise concerns. Within any semiconductor thermal application where greater than 100 W of thermal energy must be released the challenge is nearly insurmountable. For example in LED fixtures currently on the market if 150 W of thermal power must be dissipated the heat sink alone can weigh upwards of 50 lbs. This far exceeds the weight limit for MH fixture mogul base which must be less than 5 lbs.
The Loop Heat Pipe (LHP) is a two-phase heat-transfer device with capillary pumping of the working fluid that is utilized in the ILF for thermal control of extreme brightness LED arrays. The LHP device consists of an evaporator, a condenser, a liquid reservoir, and separate liquid and vapor lines. In operation the liquid medium is converted to vapor at the evaporator and is then converted back to a liquid at the condenser so that the heat at the evaporator is mostly converted into latent heat of phase transformation and is dumped at the condenser by the reverse process in an essentially adiabatic process. The pressure of vaporization is larger than the pressure of condensation, and hence the vapor flows from the evaporator to the condenser with no additional power input. Consequently, the LHP is passive in that it operates on waste heat. This passive transport of a working fluid is achieved by capillary pumping of a wick structure, which is located in the evaporator. The wick can act as the “engine” in the LHP as long as the external pressure drop in the loop does not exceed the internal pressure drop across the wick structure (resulting from the wetting hydrophilic nature of the interior of the wick surface causing a meniscus film across the wick structure). The entire cycle of evaporation and condensation occurs in this sealed, evacuated loop.
The flat evaporator architecture of LHP is created to quickly integrate with extreme brightness LED modules. The attachment is made with a thermal interface material between a metal core board and the evaporator packaging plane. This quickly reconfigurable connection is both low thermal resistance and easily reworked.